The requirement of conformal invariance leads to target space dimensions higher than four. Dimensional reduction is employed [1]}, [2]}, [3]} in order to make contact with the currently observed universe. On spacetime reduction to four dimensions, the bosonic part of the (four space-time dimensional) effective action, \(S_B\) , reads in the Einstein frame [4]}, [5]}, [6]}:

SB = 122d4x-g(R - e-4HH - ) + ...,

where
\(H_{\mu \nu \rho } = \partial _{[\mu }\, B_{\nu \rho ]},\) 
